What’s the real theory/science behind use of a concave nose on a longboard? Lift, control, funnel air under the board, something else?
I have a hard time seeing how a concave shape would generate lift directly, but you don’t know what you don’t know and I’ve been wrong before.
Control? The edge of the concave area providing a little more bite into the face? I can maybe see that.
Funnel air? Not sure where I heard that but thought I’d include it.
It isn’t thust - not with the physics or thermodynamics I was taught.
Other?
It seems to me that a flat underside with suitable nose (and overall board) rocker for wave size and speed would plane (provide lift) at the lowest speed/most efficiently, at least on flat water. Any deviation from that (concave, Vee, whatever) would reduce lift, I’d think. Maybe non-flat shapes provide other benefits but I don’t see how lift is one of them.
My 9-10 Con Pin has a concave nose. A Weber 68 Performer I saw the other day had no concave. A Joel Tudor that I got a poor look at appeared to have no concave. It got me wondering about the science behind the concave nose and whether or not they really are beneficial, or if boards work in spite of them.
Just do the “Spoon in the running water” thing… Dangle a spoon between your fingers and let the round side hit the running water with your kitchen faucet on full blast. Now turn it around and dangle the spoon side in the water. Get it now?
Thanks for the tips soulstice. I had read both, and several others, before posting and they are in part the genesis of my Qs. What I’m looking for is more the technical rational behind concave/no concave. To some degree, and based on the descriptions of others, I can extrapolate what concave/no concave does, though there is a fair bit of difference in opinion. I may be looking for a too-simple, one dimensional explaination of what concave does; like lift. I’ve heard some opine that concave provides lift. I don’t have the experience to agree with, or take issue with, that statement but it isn’t consistant with my modest understanding of fluid dynamics. But, it may be more multidimensional/inter-related than that and I’d guess there aren’t that many folks who have made otherwise identical boards and surfed them in various conditions, noting the differences.
The descriptions in those threads, and similar, are interesting but I still come up short. It’s sounding like a little bit control (wave face bite?) particlarly in sloppy surf, a little bit bleeding energy, all coupled with suitable rocker throughout, to provide a particular style of riding.
The North Florida East Coast has had a nice run of small waves for the past month or so. I managed to get away to St Augustine for a couple of days this past W/E. It was very nice.
Not near the sink but I think the concave shape would suck the nose down. That would make sense to me anyway, hence the training wheels others have described. Thanks.
Just do the “Spoon in the running water” thing… Dangle a spoon between your fingers and let the round side hit the running water with your kitchen faucet on full blast. Now turn it around and dangle the spoon side in the water. Get it now?
That trick always convinces me that noseriders should have belly in the front & concave in the tail.
This is how I see the effects of concave under the nose ( not the channels that Rich Harbour puts under his noses)
When you move forward on the board you increase speed.
When noseriding you need to stay in the sweet spot of the wave with the tail in the curl.
Now…when you run up to the nose the board wants to speed up but the concave actually pushes water and slows the board down as to keep the tail in the curl of the wave, at the same time the energy in the curl wants to push the board forward, so you get locked in.
Now depending on the wave you may need the speed to make it through faster sections while on the nose
then a flat nose would be the way to go.
If the conditions were a bit choppy then a bellied nose would be the choice, as it would slide through the chop
These pro’s like Tudor (especially) know their equipment and can read the surf conditions ( sixth sense)
by choosing the correct board for the conditions they look soooooooo smooooooth.
I put 'em in sometimes for decoration, but I don’t believe they help. If you look at the water flow and the general shallowness of concaves, they don’t hold or channel water worth a damn. Remember, each change in water flow direction costs energy. But then I’m kind of irritable now and then; with good reason given all the crap that has been foisted in my (and your) general direction by magazines and hypesters trying to sell the living shite out of each “new thing”.
And one more thing: what the pros ride is of very little consequence to the rest of us. Where there’s money involved, it speaks the loudest.
A blended concave that blends to the middle of the board affectively flattens the entry rocker possibly making the front of the board faster.
A tear drop concave with a relatively hard edge, may direct water flow down in turn pushing the nose up and slowing the board down from the plowing effect of the reverse curve of the transition point.
Concaves also reduce the thickness and thus the swing weight of the board.
These are all small effects and as with all other aspects of surfboard design it is the collection of the design elements that dictate the result, not a single elemment.
As for scientific explanation, I’d say concaves are in the art department not the science department in that no-one seems to really know what they are doing. Lots of theory At least that is the impression I have gotten from talking to some of the shapers recognized as building some of the best noseriders.
Benny, what am I missing… The spoon in the faucet trick tells me concave nose and belly tail. The belly tail has the water flowing over the curve creating suction down into the water (lift just downwards, like an inverted airplane wing) and the concave is like the water hitting the dished out side of the spoon and because the water does not flow around it but rather deflects the spoon it should be deflecting the nose away from the flow, and thus up out of the wave.
Benny many moons ago suggested to go with no concave on my 10’6" log that I built and have grown to love. I have to say on east coast conditions where fast breaking waves and close outs have to be factored in, my board locks in well when in the pocket only. My board is on the flatter side with 3.25" nose rocker and 3.75" tail rocker with a moderately bellied bottom. Obviously tail kick, rails, rocker break point, fin size and set up, parallel rails or hips, and many other design concepts have to be factored in, but mine seems to work really well.
I also did a 10’8" with 4" of late tail rocker and 5" of late nose rocker with a double concave deepest one foot from the nose. This board stalls well when riding on the shoulder until the wave catches up, then seems to “stick” with the pocket. It has slipped out on me on occasion when surfing faster waves though.
I know there are different theories and debates about what concaves do, but I think there are far more many design choices that have an effect on what a concave actually does.
concave won’t make you noseride. its just a preference. I cant stand it. takes away from smooth forward trim. takes away from glide. doesn’t give me any more tip time either. when im doing a 5, because im not to totally in the pocket, it helps a bit. but when in the pocket ready to stand on the nose completely, it doesn’t do anything for me.
i like belly in the nose. lets it sit in the water and not budge.
